1. Field of the Invention
The present invention relates to a variable air volume control apparatus for adjusting the volume of air supplied indoors appropriately in accordance with a set temperature of a room thermometer.
2. Description of the Related Art
In general, a variable air volume control apparatus is an important component in a variable air volume control system, which adjusts air volume to change room temperature, thereby maintaining pleasant indoor environment as well as preserving energy.
In such a variable air volume control apparatus, an air volume change ratio curve in accordance with an opening ratio of a damper is an important factor for adjusting the air volume according to temperature change indoors.
Therefore, the present invention aims to significantly improve the air volume change ratio curve such that it is changed from a conventional non-linear form to a linear form to realize precise control of the air volume.
FIGS. 1 and 2 illustrate a conventional variable air volume control apparatus, in which a circular plate-shaped damper blade construction 230, hereinafter referred to more simply as a damper blade or damper plate, is installed to be rotatable about a shaft 232 in a cylindrical duct 210. The conventional variable air volume control apparatus controls air volume through a following process.
A room thermometer 250 (not shown in detail) installed indoors senses room temperature and transmits information thereof (a signal) to a controller 260 (not shown in detail). The controller 260 which received the information computes the information and currently set temperature from the room thermometer 250 to calculate the air volume needed.
Then, the controller transmits a signal for an open angle corresponding to the air volume needed, to operational devices such as a motor or an actuator 240 which are then operated accordingly. Also, the controller measures the air volume at an inlet side via an air volume measurement device such as an anemometer or a differential pressure sensor installed at the inlet side and transmits the information (signal) to the controller 260.
The controller 260 receives the information (signal) from the air volume measurement device and rotates the shaft 232 of the operational device as much as the excessive or deficient amount of air to adjust the open angle of the damper blade 230, thereby maintaining the air volume corresponding to the information (signal) from the room thermometer 250.
As the damper blade 230 is operated, a viewer looking through the air duct from the air input side near the air volume measurement device, such as above flow sensor 220 in the air duct, can see changes in the open air area above and around the leading edge of the damper blade 230 and below and around the trailing edge of the damper blade 230. Such open air area, designated Aopen, is a function of the angle θ, with no open air area when the damper blade is fully closed at an angle θ=0° and with essentially a completely open air area when the damper blade 230 is fully opened at an angle θ=90°. At smaller opening ratios of θ/90°, that is, when the damper blade is opened at only small angles θ relative to the fully opened 90° position, the open air area that results is less than what results at larger opening ratios.
When the radius of the damper blade, designated rdamper, and the radius of the air duct, designated Rduct, are the same, it can be shown by the application of geometric formulas and mathematical calculations that the height of the open air area between the leading edge of the damper blade at its peak and the peak of the interior surface of the air duct, which measurement is here designated y for convenience of reference, is a function of the radius of the damper plate 230 and the angle θ, that may be conveniently expressed as y=rdamper(1−cos θ), with the open air ratio thus corresponding to y/rdamper=(1−cos θ).
However, the conventional air volume control apparatus 200 as shown in FIG. 1 is less than ideal in its operation, especially in that the resultant air volume change ratio, shown as plot C in FIG. 3, is a greatly deviating (distorted) curve rather than a line. Such distortion is a consequence of the non-linear characteristic of the open air ratio y/rdamper relative to the opening ratio θ/90°, as represented by plot B of FIG. 3, as well as factors such as air overflow and friction between air flow and the inner surface of duct 210.
As shown in FIG. 3, the open area ratio curve B deviates greatly from the opening ratio line A, and thus the volume of air flowing through a corresponding open air area is far from being in direct proportion to the corresponding opening ratio. Therefore, the air volume change ratio C results in a curve which greatly deviates from the opening ratio line A.
As seen from the air volume change ratio curve, in a low opening ratio range of about 0 to 30%, i.e., in the range D1 of near closed state of the damper blade, the air volume change is too small with respect to the corresponding change of the opening ratio, thus difficult to adjust the air volume in this range. Also, in a high opening ratio range of about 70 to 100%, i.e., in the range D2 of near open state of the damper blade, the air volume change is too small with respect to the corresponding opening ratio, thus difficult to accurately and precisely adjust the air volume.
In addition, in the opening ratio range of 30% to 70%, the air volume changes drastically with respect to even a small change in the open angle, i.e., the opening ratio of the damper blade, hindering precise control of the air volume.
Therefore, in order to exclude the tendency of too small an air volume change with respect to the opening ratio in the range D1 of near closed state of the damper blade and achieve a linear form in the entire range of the opening ratio, in the conventional air volume control apparatus shown in FIG. 2, the damper blade 230 installed with the shaft 232 inside the duct 210 is modified into an oval plate shape and the closed position of the damper blade in the duct 210 is shifted about 30 degrees to an angle θ1 so that an adjustable range of angle θ2 is thereby shifted to be 30 degrees to 90 degrees.
Shifting the adjustable range of angle θ2 of the damper blade 230 to be from 30 degrees to 90 degrees, where an adjustable range is from 0 degrees to 60 degrees to yield 0% to 100% of air volume change, results in a drawback in which the adjustable range of angle is decreased by 33% from that with an adjustable range of 0 to 90 degrees to yield 0 to 100% of air volume change.
This means that the adjustable range of angle is too small to allow precise control of air volume.
Therefore, rather than reducing the adjustable angle range of the variable air volume control apparatus 200, the adjustable angle range of 0 to 90 degrees should be maintained to yield the air volume change of 0 to 100% in order to more accurately and precisely control the air volume.
Also, in order to change the air volume curve into a linear form, the open area should be increased at the low opening ratio.
This allows obtaining a linear air volume change in proportion to the opening ratio of the damper blade at a low opening ratio, thereby accurately and precisely controlling the air volume.
As confirmed above, the flow control damper is an essential component for adjusting the air volume introduced into the variable air volume control apparatus in an air conditioning system adopting a variable air volume control system. The capability of the flow control damper to linearly control the air volume plays a determining role in efficiently operating the variable air volume control apparatus.
Recently, the controller for the variable air volume control apparatus has been developed into a finely-operated electronic type, which is used in almost all air conditioning systems. However, if the variable air volume control apparatus does not have a linear flow characteristics of the flow control damper operated by the actuator 240, precise control of the variable air volume control apparatus cannot be efficiently realized, regardless of excellent capabilities and control of the controller of the variable air volume control apparatus and the highly accurate and reliable flow sensor for sensing air volume change at an inlet side of the variable air volume control apparatus or constant feedback control of the flow control damper by comparing and computing differential pressure signal from the flow sensor with the indoor temperature load change.
Air flows at the highest velocity in the central portion of a duct or conduit, and at a low velocity near the wall due to friction. Thus, when the damper blade is opened at the opening ratio of 100%, although the velocitymay somewhat change, the air volume flowing per unit of time approximates to 100% with substantially no inflow or outflow loss.
When the damper blade's opening ratio decreases by 50%, i.e., the damper blade 230 is biased at 45 degrees, the air volume is also supposed to be decreased by 50%. However, the actual air volume turns out to be less than 50%. This is because when the damper blade 230 is biased at 50% (45 degrees) in a cylindrical duct, the resultant open area ratio is too small at 29.29%, and thus the resultant air volume is also small at about 40% (see FIG. 3).
Also, when the opening ratio of the damper blade is 30% or less, the resultant open area ratio is too small at 10% or less with too small an air volume, hindering precise control.
In addition, when the open angle of the damper blade 230 is 70% or more, the resultant open area is smaller than the directly proportional line whereas too large a volume of air flows, hindering precise control.
As described above, in the conventional variable air volume control apparatus 200, the air volume change with respect to the opening ratio of the damper blade 230 turns out to be a greatly deviating (distorted) curve C as shown in FIG. 3, rather than a line.
In FIG. 3, the graph shows the open area ratio and air volume change ratio with respect to the opening ratio, obtained by the above conventional variable air volume control apparatus.
Therefore, as shown in the graph in FIG. 3, with the conventional air volume control apparatus 200, in the opening ratio range of 30% to 40% or less, the actual open area ratio curve B deviates greatly from the ideal open area ratio, i.e., line A which is in direct proportion to the opening ratio of the damper blade 230. As a result, accurate control of air volume is difficult.
Therefore, the conventional air volume control apparatus 200 cannot accurately control the air volume introduced indoors, thus having difficulty in supplying fresh air indoors while consuming more energy.
In order to overcome such a problem, Korean Utility Model Registration No. 0346769 (entitled “Dome Type Air Damper Unit”) has been suggested. This conventional dome type air damper unit has a cylindrical body having flanges at opposed ends thereof. Inside the body, a wing unit, connected to a control unit, is connected to a plurality of wings at one side of the body, forming a dome-shape. The control unit adjusts the angle of the wings to operate the plurality of wings simultaneously, thereby changing an open area of an air outlet to adjust the air volume.
However, this conventional structure is structurally complex and expensive, yielding a non-linear air volume characteristics curve.
A different conventional technology has been suggested in Korean Utility Model Registration No. 0376799 (entitled “Variable Air Volume Control Apparatus”).
In this conventional variable air volume control apparatus, a shaft is disposed movable back and forth and connected to a guide lever of a damper actuator disposed outside of the apparatus body and operated by a room thermometer. Also, a pair of symmetrical air volume control dampers are split or joined in accordance with the movement of a pair of links that are connected to an end of the shaft. And an air conduit is installed to connect between an air inlet and a first air outlet, and is connected to a mixed air outlet.
However, this structure is structurally complex, thus difficult to manufacture, and expensive. Further, it uses a guide lever in a link structure, which makes noise and the resultant air volume change ratio curve has non-linear characteristics.
A different structure from the above is disclosed in U.S. Pat. No. 5,333,835 (entitled “Electric Motor Driven Air Valve”).
In this structure, a screw shaft is rotated by a motor to thereby move a damper blade connected to the screw shaft, adjusting the volume of air flowing between the open damper blade and the duct.
However, it is also difficult to accurately adjust the air volume according to the orbit of the damper blade with this conventional structure which is expensive and difficult to manufacture due to structural complexity.